Boundary acoustic wave device

ABSTRACT

Aspects of this disclosure relate to an acoustic wave device that includes high velocity layers on opposing sides of a piezoelectric layer. A temperature compensation layer can be positioned between one of the high velocity layers and the piezoelectric layer. The acoustic wave device can be arranged to generate a boundary acoustic wave having a higher velocity than a respective acoustic velocity of each of the high velocity layers.

CROSS REFERENCE TO PRIORITY APPLICATION

This application claims the benefit of priority under 35 U.S.C. § 119(e)of U.S. Provisional Patent Application No. 62/659,568, filed Apr. 18,2018 and titled “ACOUSTIC WAVE DEVICE WITH MULTI-LAYER PIEZOELECTRICSUBSTRATE,” the disclosure of which is hereby incorporated by referencein its entirety herein.

BACKGROUND Technical Field

Embodiments of this disclosure relate to acoustic wave devices.

Description of Related Technology

Acoustic wave filters can be implemented in radio frequency electronicsystems. For instance, filters in a radio frequency front end of amobile phone can include acoustic wave filters. A plurality of acousticwave filters coupled to a common node can be arranged as a multiplexer.For example, two acoustic wave filters can be arranged as a duplexer.

An acoustic wave filter can include a plurality of acoustic waveresonators arranged to filter a radio frequency signal. Example acousticwave filters include surface acoustic wave (SAW) filters and bulkacoustic wave (BAW) filters. A surface acoustic wave resonator caninclude an interdigital transducer electrode on a piezoelectricsubstrate. The surface acoustic wave resonator can generate a surfaceacoustic wave on a surface of the piezoelectric layer on which theinterdigital transducer electrode is disposed. A surface acoustic wavedevice can include a cavity on the surface of a chip on which a surfaceacoustic wave propagates.

A boundary acoustic wave resonator can concentrate acoustic energy neara boundary of two attached materials of the boundary acoustic wavedevice. Boundary acoustic wave resonators can be implemented without acavity over the surface of a chip that generates a boundary acousticwave.

SUMMARY OF CERTAIN INVENTIVE ASPECTS

The innovations described in the claims each have several aspects, nosingle one of which is solely responsible for its desirable attributes.Without limiting the scope of the claims, some prominent features ofthis disclosure will now be briefly described.

One aspect of this disclosure is an acoustic wave device that includes apiezoelectric layer, an interdigital transducer electrode on thepiezoelectric layer, high velocity layers on opposing sides of thepiezoelectric layer, and a low velocity layer positioned between thepiezoelectric layer and a first high velocity layer of the high velocitylayers. The low velocity layer has a lower acoustic velocity than thehigh velocity layers. The acoustic velocity is the speed of sound of ashear wave propagating in a solid. The acoustic wave device isconfigured to generate a boundary acoustic wave such that acousticenergy is concentrated at a boundary of the piezoelectric layer and thelow velocity layer.

Each of the high velocity layers can have a higher acoustic velocitythan a velocity of the boundary acoustic wave. The velocity of theboundary acoustic wave can be in a range from 2500 meters per second to4800 meters per second. The velocity of the boundary acoustic wave canbe in a range from 4100 meters per second to 4800 meters per second.

The low velocity layer can include silicon dioxide. The high velocitylayers can be silicon layers.

At least one of the high velocity layers can be a silicon layer. Atleast one of the high velocity layers can include at least one ofsilicon nitride, aluminum nitride, diamond, quartz, or spinel. The highvelocity layers can be made of the same material as each other.

The boundary acoustic wave has a wavelength of λ. With a thickness of atleast 1λ, the boundary acoustic wave can be confined at the boundary ofthe piezoelectric layer and the low velocity layer. At least one of thehigh velocity layers can have a thickness in a range from 1λ to 10λ. Atleast one of the high velocity layers can have a thickness in a rangefrom 1λ to 5λ. In some instances, one or both of the high velocitylayers can have a thickness of greater than 10λ. The piezoelectric layercan have a thickness of less than 2λ. The piezoelectric layer can be alithium tantalate layer. The piezoelectric layer can be a lithiumniobate layer.

Another aspect of this disclosure is a radio frequency module thatincludes an acoustic wave filter configured to filter a radio frequencysignal and a radio frequency switch coupled to the acoustic wave filter.The radio frequency switch is packaged with the acoustic wave filter.The acoustic wave filter includes an acoustic wave device including apiezoelectric layer, an interdigital transducer electrode on thepiezoelectric layer, high velocity layers on opposing sides of thepiezoelectric layer, and a low velocity layer disposed between thepiezoelectric layer and a first high velocity layer of the high velocitylayers. The low velocity layer has a lower acoustic velocity than thehigh velocity layers. The acoustic wave device is configured to generatea boundary acoustic wave such that acoustic energy is concentrated at aboundary of the piezoelectric layer and the low velocity layer.

The radio frequency module can include a power amplifier, in which theradio frequency switch is configured to selectively electrically connectan output of the power amplifier to the acoustic wave filter. The radiofrequency module can include an antenna port, in which the radiofrequency switch is configured to selectively electrically connect theacoustic wave filter to an antenna port of the radio frequency module.

Another aspect of this disclosure is a method of filtering a radiofrequency signal with an acoustic wave filter. The method includesproviding a radio frequency signal to an acoustic wave filter andfiltering the radio frequency signal with the acoustic wave filter. Theacoustic wave filter includes an acoustic wave device that includes apiezoelectric layer, an interdigital transducer electrode on thepiezoelectric layer, high velocity layers on opposing sides of thepiezoelectric layer, a low velocity layer positioned between thepiezoelectric layer and a first high velocity layer of the high velocitylayers. The low velocity layer having a lower acoustic velocity than thehigh velocity layers. The acoustic wave device generating a boundaryacoustic wave such that acoustic energy is concentrated at a boundary ofthe piezoelectric layer and the low velocity layer.

The high velocity layers can be silicon layers and the low velocitylayer can be a silicon dioxide layer. The piezoelectric layer can be alithium niobate layer or a lithium tantalate layer.

Another aspect of this disclosure is an acoustic wave device thatincludes a piezoelectric layer, an interdigital transducer electrode onthe piezoelectric layer, high velocity layers on opposing side of thepiezoelectric layer, and a temperature compensation layer positionedbetween the first high velocity layer and the piezoelectric layer. Thehigh velocity layers include a first high velocity layer having a firstacoustic velocity and a second high velocity layer having a secondacoustic velocity. The acoustic wave device is configured to generate aboundary acoustic wave having a velocity that is less than both thefirst acoustic velocity and the second acoustic velocity.

The first acoustic velocity can be substantially the same as the secondacoustic velocity. The first acoustic velocity can be different than thesecond acoustic velocity.

The first high velocity layer can be a silicon layer. The second highvelocity layer can be a second silicon layer. The first high velocitylayer can include at least one of silicon nitride, aluminum nitride,diamond, quartz, or spinel. The piezoelectric layer can be either alithium tantalate layer or a lithium niobate layer. The temperaturecompensation layer can include silicon dioxide.

The boundary acoustic wave has a wavelength of λ. The first highvelocity layer can have a thickness in a range from 1λ, to 10λ. Thepiezoelectric layer can have a thickness of less than 2λ.

The interdigital transducer electrode is can be contact with thepiezoelectric layer on a side of the piezoelectric layer facing thetemperature compensation layer. The interdigital transducer electrodecan be in contact with the piezoelectric layer on a side of thepiezoelectric layer that is opposite to the temperature compensationlayer.

Another aspect of this disclosure is an acoustic wave device thatincludes a piezoelectric layer, an interdigital transducer electrode onthe piezoelectric layer, silicon layers on opposing sides of thepiezoelectric layer, and a silicon dioxide layer disposed between one ofthe silicon layers and the piezoelectric layer. The acoustic wave deviceis configured to generate a boundary acoustic wave at an interface ofthe piezoelectric layer and the interdigital transducer electrode.

The boundary acoustic wave has a wavelength of λ. The silicon layers caneach have a thickness in a range from λ to 10λ. The piezoelectric layercan have a thickness of no greater than 2λ.

The piezoelectric layer can be a lithium tantalate layer. Thepiezoelectric layer can be a lithium niobate layer.

The interdigital transducer electrode can be on a side of thepiezoelectric layer facing the silicon dioxide layer. The interdigitaltransducer electrode can be on a side of the piezoelectric layeropposite to the silicon dioxide layer.

Another aspect of this disclosure is an acoustic wave filter comprisingan acoustic wave device that includes a piezoelectric layer, aninterdigital transducer electrode on the piezoelectric layer, siliconlayers on opposing sides of the piezoelectric layer, and a silicondioxide layer disposed between one of the silicon layers and thepiezoelectric layer. The acoustic wave device is configured to generatea boundary acoustic wave. The acoustic wave filter is configured tofilter a radio frequency signal.

Another aspect of this disclosure is an acoustic wave device assemblythat includes a first die and a second die stacked with the first die.The first die includes a first acoustic wave device configured togenerate a boundary acoustic wave. The first acoustic wave deviceincludes a piezoelectric layer, an interdigital transducer electrode onthe piezoelectric layer, and high acoustic velocity layers on opposingsides of the piezoelectric layer. The high acoustic velocity layers eachhave an acoustic velocity that is greater than a velocity of theboundary acoustic wave. The second die includes a second acoustic wavedevice configured to generate a second boundary acoustic wave.

The acoustic wave device assembly can include a third die stacked withthe first die and the second die, in which the third die can includes athird acoustic wave device configured to generate a third boundaryacoustic wave.

The first acoustic wave device can include a temperature compensationlayer disposed between the piezoelectric layer and a first high acousticvelocity layer of the high acoustic velocity layers.

A first high acoustic velocity layer of the high acoustic velocitylayers can be a silicon layer. A first high acoustic velocity layer ofthe high acoustic velocity layers can include at least one of siliconnitride, aluminum nitride, diamond, quartz, or spinel.

The first acoustic wave device can be included in a first acoustic wavefilter, and the second acoustic wave device can be included in a secondacoustic wave filter.

The acoustic wave device assembly can include a via extending throughthe first die. The acoustic wave device assembly can include a wire bondextending from the second die.

The first die can be electrically isolated from the second die. Theacoustic wave device assembly can include an air gap between the firstdie and the second die. The acoustic wave device assembly can include adielectric material disposed between the first die and the second die.The acoustic wave device assembly can include a dielectric material anda metal shield disposed between the first die and the second die.

The second acoustic wave device can include a second piezoelectriclayer, a second interdigital transducer electrode on the secondpiezoelectric layer, and second high acoustic velocity layers onopposing sides of the second piezoelectric substrate, in which thesecond high acoustic velocity layers each have an acoustic velocity thatis greater than a velocity of the second boundary acoustic wave.

Another aspect of this disclosure is a radio frequency module withacoustic wave filters. The radio frequency module includes a firstacoustic wave filter configured to filter a first radio frequencysignal, a second acoustic wave filter configured to filter a secondradio frequency signal, and a package enclosing the first acoustic wavefilter and the second acoustic wave filter. The first acoustic wavefilter includes a first acoustic wave device on a first die andconfigured to generate a boundary acoustic wave. The first acoustic wavedevice includes a piezoelectric layer and high acoustic velocity layerson opposing sides of the piezoelectric layer, in which the high acousticvelocity layers each have an acoustic velocity that is greater than avelocity of the boundary acoustic wave. The second acoustic wave filterincluding a second acoustic wave device on a second die and configuredto generate a second boundary acoustic wave. The second die is stackedwith the first die.

A thickness of the radio frequency module can be less than 300micrometers.

A duplexer can include the first acoustic wave filter and the secondacoustic wave filter.

The radio frequency module can include a radio frequency switch coupledto the first acoustic wave filter and the second acoustic wave filter,in which the radio frequency switch being enclosed within the package.

Another aspect of this disclosure is a wireless communication devicethat includes an antenna and acoustic wave filters in communication withthe antenna. The acoustic wave filters are configured to filter radiofrequency signals. The acoustic wave filters include a first die stackedwith a second die. The first die includes a first acoustic wave deviceconfigured to generate a boundary acoustic wave. The first acoustic wavedevice includes a piezoelectric layer disposed between two high acousticvelocity layers having acoustic velocities that are higher than avelocity of the boundary acoustic wave.

The wireless communication device can include a transceiver incommunication with the acoustic wave filters. The wireless communicationdevice can include a radio frequency switch, the acoustic wave filtersarranged as a multiplexer that is coupled to the radio frequency switch.

For purposes of summarizing the disclosure, certain aspects, advantagesand novel features of the innovations have been described herein. It isto be understood that not necessarily all such advantages may beachieved in accordance with any particular embodiment. Thus, theinnovations may be embodied or carried out in a manner that achieves oroptimizes one advantage or group of advantages as taught herein withoutnecessarily achieving other advantages as may be taught or suggestedherein.

The present disclosure relates to U.S. patent application Ser. No.______ [Attorney Docket SKYWRKS.871A1], titled “ACOUSTIC WAVE DEVICEWITH MULTI-LAYER PIEZOELECTRIC SUBSTRATE,” filed on even date herewith,the entire disclosure of which is hereby incorporated by referenceherein. The present disclosure also relates to U.S. patent applicationSer. No. ______ [Attorney Docket SKYWRKS.871A3], titled “ACOUSTIC WAVEDEVICES ON STACKED DIE,” filed on even date herewith, the entiredisclosure of which is hereby incorporated by reference herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of this disclosure will now be described, by way ofnon-limiting example, with reference to the accompanying drawings.

FIG. 1 illustrates a cross sectional view of an acoustic wave deviceaccording to an embodiment.

FIG. 2 illustrates a cross sectional view of an acoustic wave device anda simulated acoustic displacement distribution according to anembodiment.

FIG. 3A illustrates a cross sectional view of an acoustic wave deviceaccording to an embodiment.

FIG. 3B illustrates a cross sectional view of an acoustic wave deviceaccording to an embodiment.

FIG. 3C illustrates a graph comparing performance of the acoustic wavedevices of FIGS. 3A and 3B.

FIG. 4A illustrates a cross sectional view of an acoustic wave deviceaccording to an embodiment.

FIG. 4B illustrates a cross sectional view of an acoustic wave deviceaccording to another embodiment.

FIG. 4C illustrates a cross sectional view of an acoustic wave deviceaccording to another embodiment.

FIG. 4D illustrates a cross sectional view of an acoustic wave deviceaccording to another embodiment.

FIG. 4E illustrates a cross sectional view of an acoustic wave deviceaccording to another embodiment.

FIG. 4F illustrates a cross sectional view of an acoustic wave deviceaccording to another embodiment.

FIG. 4G illustrates a cross sectional view of an acoustic wave deviceaccording to another embodiment.

FIG. 5 illustrates another cross sectional view of an acoustic wavedevice according to an embodiment.

FIG. 6A illustrates an acoustic wave device assembly of stacked acousticwave devices with a via extending through an acoustic wave deviceaccording to an embodiment.

FIG. 6B illustrates an acoustic wave device assembly of stacked acousticwave devices with an air gap between acoustic wave devices and a viaextending through an acoustic wave device according to an embodiment.

FIG. 6C illustrates an acoustic wave device assembly of stacked acousticwave devices with dielectric material between acoustic wave devices anda via extending through an acoustic wave device according to anembodiment.

FIG. 6D illustrates an acoustic wave device assembly of stacked acousticwave devices with dielectric material and a metal shield betweenacoustic wave devices and a via extending through an acoustic wavedevice according to an embodiment.

FIG. 6E illustrates an acoustic wave device assembly of stacked acousticwave devices with wire bonds extending from acoustic wave devicesaccording to an embodiment.

FIG. 7A is a schematic block diagram of a module that includes a filterand an antenna switch according to an embodiment.

FIG. 7B is a schematic block diagram of a module that includes a poweramplifier, a switch, and a filter according to an embodiment.

FIG. 7C is a schematic block diagram of a module that includes poweramplifier, a switch, a filter, and an antenna switch according to anembodiment.

FIG. 8 is a schematic block diagram of a wireless communication devicethat includes a filter in accordance with one or more embodiments.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

The following description of certain embodiments presents variousdescriptions of specific embodiments. However, the innovations describedherein can be embodied in a multitude of different ways, for example, asdefined and covered by the claims. In this description, reference ismade to the drawings where like reference numerals can indicateidentical or functionally similar elements. It will be understood thatelements illustrated in the figures are not necessarily drawn to scale.Moreover, it will be understood that certain embodiments can includemore elements than illustrated in a drawing and/or a subset of theelements illustrated in a drawing. Further, some embodiments canincorporate any suitable combination of features from two or moredrawings.

Acoustic wave filters can filter radio frequency (RF) signals in avariety of applications, such as in an RF front end of a mobile phone.An acoustic wave filter can be implemented with surface acoustic wave(SAW) devices. SAW devices can include an air cavity above a surface onwhich a surface acoustic wave propagates. The air cavity can add to theheight and/or volume of SAW device chips. The size of SAW device chipscontributes to the overall size of a packaged component.

Boundary acoustic wave devices can be implemented without air cavities.This can reduce package size relative to implementing SAW devices thatinclude an air cavity. However, boundary acoustic wave devices haveencountered difficulty in confining acoustic waves within the device.Moreover, implementing relatively thin boundary acoustic wave deviceshas been challenging.

Aspects of this disclosure relate to a multi-layer piezoelectric devicethat includes high velocity layers on opposing sides of a piezoelectriclayer. The high velocity layers each have an acoustic velocity that ishigher than an acoustic velocity of an acoustic wave generated by themulti-layered piezoelectric device. As used herein, “acoustic velocity”can be the speed of sound of a shear wave propagating in a solid. Thehigh velocity layers can improve confinement of the acoustic wave withinthe device. As an example, the high velocity layers can be siliconlayers in certain applications. The multi-layer piezoelectric device caninclude a low velocity layer between the piezoelectric layer and one ofthe high velocity layers. The low velocity layer has a lower acousticvelocity than the high velocity layers. The low velocity layer can be atemperature compensation layer. For example, the low velocity layer canbe a silicon dioxide layer. The multi-layer piezoelectric device cangenerate a boundary acoustic wave and be implemented as a relativelythin device. The multi-layered piezoelectric device can have a thicknesson the order of a wavelength of the boundary acoustic wave generated bythe device in certain applications.

FIG. 1 illustrates a cross sectional view of an acoustic wave device 10according to an embodiment. The acoustic wave device 10 can generate aboundary acoustic wave. Accordingly, the acoustic wave device 10 can bereferred to as a boundary wave device. The acoustic wave device 10 canhave a relatively small height and confine the boundary acoustic wavewithin the acoustic wave device 10. As illustrated, the acoustic wavedevice 10 includes a piezoelectric layer 12, an interdigital transducer(IDT) electrode 14, a temperature compensation layer 16, a first highvelocity layer 17, and a second high velocity layer 18.

The acoustic wave device 10 is configured to generate a boundaryacoustic wave having acoustic energy concentrated at an interface of thepiezoelectric layer 12 and the temperature compensation layer 16. Theboundary acoustic wave can have a velocity a range from 2500 meters persecond to 4800 meters per second. In certain instances, the boundaryacoustic wave can have a velocity above 3900 meters per second. In somesuch instances, the boundary acoustic wave can have a velocity above4100 meters per second. The velocity of the boundary acoustic wave canbe in a range from 3900 meters per second to 4800 meters per second. Insome instances, the velocity of the boundary acoustic wave is in a rangefrom 4100 meters per second to 4800 meters per second.

The piezoelectric layer 12 can be any suitable piezoelectric layer forgenerating an acoustic wave having a wavelength λ. For example, thepiezoelectric layer can be a lithium based piezoelectric layer, such asa lithium tantalate (LiTaO₃) layer or a lithium niobate (LiNbO₃) layer.The illustrated piezoelectric layer 12 has a thickness H₁. The thicknessH₁ can be on the order of the wavelength λ. The thickness H₁ can be in arange from about 0.1λ to 5λ. Such a thickness can be sufficiently thinto reduce radiation loss relative to thicker piezoelectric layers. Thethickness of the piezoelectric layer 12 can be less than 2λ, such as ina range from 0.1λ to 2λ. In certain applications, the thickness can beabout 1.0λ for a lithium tantalate piezoelectric layer or a lithiumniobate piezoelectric layer.

The IDT electrode 14 is disposed on piezoelectric layer 12. The IDTelectrode 14 can generate a boundary acoustic wave at an interface ofthe piezoelectric layer 12 and the temperature compensation layer 16.The illustrated IDT electrode 14 has a pitch L and a thickness h₁. Thepitch L can define and correspond to the wavelength λ of an acousticwave generated by the acoustic wave device 10. The thickness h₁ can bein a range from about 0.01λ to 0.15λ. For example, h₁ can be about 0.08λin certain applications. The IDT electrode 14 can include aluminum, analuminum alloy, and/or any other suitable material for an IDT electrode14. For example, IDT electrode material can include aluminum (Al),titanium (Ti), gold (Au), silver (Ag), copper (Cu), platinum (Pt),tungsten (W), molybdenum (Mo), ruthenium (Ru), or any suitablecombination thereof. IDT electrode thickness h₁ can be relativelythinner when relatively heavy electrodes, such as Au, Ag, Cu, Pt, W, Mo,or Ru, are used.

The temperature compensation layer 16 is positioned between thepiezoelectric layer 12 and the first high velocity layer 17. Asillustrated, the temperature compensation layer 16 has a first side inphysical contact with the piezoelectric layer 12 and a second side inphysical contact with the first high velocity layer 17. The temperaturecompensation layer 16 can improve the temperature coefficient offrequency (TCF) of the acoustic wave device 10 relative to a similaracoustic wave device without the temperature compensation layer 16. Thetemperature compensation layer 16 can bring the TFC of the acoustic wavedevice 10 closer to zero than the TCF of a similar acoustic wave devicethat does not include the temperature compensation layer 16. Thetemperature compensation layer 16 can have a positive temperaturecoefficient of frequency. For instance, the temperature compensationlayer 16 can be a silicon dioxide (SiO₂) layer. The temperaturecompensation layer 16 can alternatively be a tellurium dioxide (TeO₂)layer or a silicon oxyfluoride (SiOF layer). The temperaturecompensation layer 16 can include any suitable combination of SiO₂,TeO₂, and/or SiOF.

In certain applications, the temperature compensation layer 16 canimprove an electromechanical coupling coefficient k² of the acousticwave device 10. The electromechanical coupling coefficient k² for theacoustic wave device 10 can be greater than 5%. For instance, in certainembodiments, the electromechanical coupling coefficient k² is around 9%.The electromechanical coupling coefficient k² can be in a range from 5%to 15% in various applications. The acoustic wave device 10 can have anelectromechanical coupling coefficient k² of up to about 15% when thepiezoelectric layer 12 is a lithium niobate layer.

The temperature compensation layer 16 can have a lower bulk velocitythan a velocity of the acoustic wave generated by the IDT electrode 14.Accordingly, the temperature compensation layer 16 can be referred to asa low velocity layer. Such a low velocity layer has a lower acousticvelocity than the high velocity layers 17 and 18, in which the acousticvelocity of the low velocity layer is a speed of sound of a shear wavepropagating in the low velocity layer. The temperature compensationlayer 16 can have a lower acoustic impedance than the piezoelectriclayer 12. The temperature compensation layer 16 can have a loweracoustic impedance than the first high velocity layer 17. Thetemperature compensation layer 16 can be a dielectric layer.

The illustrated temperature compensation layer 16 has a thickness H₂.The thickness H₂ can be less than 1.0λ. The thickness H₂ can be in arange from about 0.05λ to 1.0λ. In some of these instances, thethickness H₂ can be less than 0.5λ.

The first high velocity layer 17 has a higher bulk velocity than avelocity of the acoustic wave generated by the IDT electrode 14. Thefirst high velocity layer 17 can have a higher acoustic impedance thanthe piezoelectric layer 12. Accordingly, the high velocity layer 17 canbe referred to as a high impedance layer. The first high velocity layer17 can have a higher acoustic impedance than the temperaturecompensation layer 16. The first high velocity layer 17 can inhibit anacoustic wave generated by the acoustic wave device 10 from leaking outof the device. The acoustic velocity of the high velocity layer 17 isthe speed of sound of a shear wave propagating in the high velocitylayer 17. The first high velocity layer 17 can be a silicon layer. Sucha silicon layer can have a relatively high acoustic velocity, arelatively large stiffness, and a relatively small density. The siliconlayer can be a polycrystalline silicon layer in certain instances. Insome other instances, the first high velocity layer 17 can beimplemented by other suitable material having a higher acoustic velocitythan the velocity of the acoustic wave generated by the IDT electrode 14of the acoustic wave device 10. For instance, the first high velocitylayer 17 can include silicon nitride, aluminum nitride, diamond such assynthetic diamond, quartz, spinel, the like, or any suitable combinationthereof.

The second high velocity layer 18 can be bonded to and in physicalcontact with the piezoelectric layer 12. The second high velocity layer18 has a higher bulk velocity than a velocity of the acoustic wavegenerated by the IDT electrode 14. Accordingly, the high velocity layer18 can be referred to as a high impedance layer. The second highvelocity layer 18 can have a higher acoustic impedance than thetemperature compensation layer 16. The second high velocity layer 18 canhave a higher acoustic impedance than piezoelectric layer 12. The secondhigh velocity layer 18 can inhibit an acoustic wave generated by theacoustic wave device 10 from leaking from the device. The acousticvelocity of the high velocity layer 18 is the speed of sound of a shearwave propagating in the high velocity layer 18. The second high velocitylayer 18 can be a silicon layer. Such a silicon layer can have arelatively high acoustic velocity, a relatively large stiffness, and arelatively small density. The silicon layer can be a polycrystallinesilicon layer in certain instances. In some other instances, the secondhigh velocity layer 18 can be implemented by other suitable materialhaving a higher acoustic velocity than the velocity of the acoustic wavegenerated by the IDT electrode 14 of the acoustic wave device 10. Forinstance, the second high velocity layer 18 can include silicon nitride,aluminum nitride, diamond such as synthetic diamond, quartz, spinel, thelike, or any suitable combination thereof.

The second high velocity layer 18 can be formed of the same material asthe first high velocity layer 17 in certain instances. The second highvelocity layer 18 can be formed of a different material than the firsthigh velocity layer 17 in some instances.

FIG. 2 illustrates a cross sectional view of an acoustic wave device 20and a simulated acoustic displacement distribution according to anembodiment. The acoustic wave device 20 is an example of the acousticwave device 10 of FIG. 1. The illustrated acoustic wave device includesa lithium tantalate layer 22, an IDT electrode 14, a silicon dioxidelayer 26, a first silicon layer 27, and a second silicon layer 28.

The acoustic displacement distribution graph shown in FIG. 2 indicatesthat acoustic energy is trapped in the lithium tantalate layer 22 andthe silicon dioxide layer 26 in the acoustic wave device 20. Theillustrated displacement distribution graph indicates that acousticenergy is concentrated at an interface of the lithium tantalate layer 22and the silicon dioxide layer 26 in the acoustic wave device 20. Thefirst silicon layer 27 has a thickness H₃. The thickness H₃ beinggreater than the wavelength λ of an acoustic wave generated by theacoustic wave device 20 can be sufficient to trap acoustic energy withinthe acoustic wave device 20. The thickness H₃ can be in a range from 1λto 10λ. In some instances, H₃ can be about 5λ. The thickness H₃ can besufficient to maintain mechanical durability of the acoustic wave device20. In such instances, the thickness H₃ can be greater than 10λ. Forexample, the thickness H₃ can be in a range from 1λ to 100λ. Thethickness H₃ can be less than 200 um, which corresponds to 100λ when λis um. With the thickness being less than 200 um, the acoustic wavedevice 20 can be thinner than certain present temperature compensatedSAW devices. As another example, the thickness H₃ can be in a range from1λ to 50λ. There is no discernable displacement on a surface of thefirst silicon layer 27 away from the lithium tantalate layer 22.Similarly, there is no discernable displacement on a surface of thesecond silicon layer 28 away from the lithium tantalate layer 22. Thethickness H₄ of the second silicon layer 28 can be similar to thethickness H₃ of the first silicon layer 27 in certain implementations.The maximum displacement in the acoustic displacement distribution iscentered on the interface of the silicon dioxide layer 26 and thelithium tantalate layer 22. The silicon dioxide layer 26 can cause theTCF to be improved. The silicon dioxide layer 26 can cause theelectromechanical coupling coefficient k² to be improved.

The general relationship shown in the acoustic displacement distributionof FIG. 2 should hold for acoustic wave devices that implement otherhigh impedance materials in place of the silicon layers 27 and/or 28, inwhich the other high impedance materials have a higher acousticimpedance than the acoustic impedance of a piezoelectric layer of thedevice. Example high impedance materials include silicon nitride,aluminum nitride, diamond such as synthetic diamond, quartz, spinel, andthe like. Similarly, the lithium tantalate layer 22 can be replaced byanother suitable piezoelectric layer, such as a lithium niobate layer,and such an acoustic wave device can function similarly to the acousticwave device 20 of FIG. 2.

In the example distribution graph of FIG. 2, an acoustic wave based onShear Horizontal (SH) mode is excited using lithium tantalate in 42°rotation Y-cut X propagation as a piezoelectric layer. However, even ifdifferent piezoelectric substrate cut angles and/or piezoelectricmaterials were used with the vibration component-based mode in thelongitudinal direction and in the thickness direction for excitation, aslong as the acoustic velocity relationship is satisfied, such a devicecan function similarly as the acoustic wave device 20 of FIG. 2.

FIG. 3A illustrates a cross sectional view of an acoustic wave device 30according to an embodiment. The acoustic wave device 30 is like theacoustic wave device 20 of FIG. 2 except that the IDT electrode isdisposed on a different surface of the lithium tantalate layer 22 andthe IDT electrode is an aluminum IDT electrode 34 in the acoustic wavedevice 30. As illustrated, the aluminum IDT electrode 34 in FIG. 3A ison a surface of the lithium tantalate layer 22 that is facing the secondsilicon layer 28.

FIG. 3A illustrates that certain acoustic wave devices can include ahigh velocity layers on opposing sides of a piezoelectric layer and alow velocity layer on an opposite side of a piezoelectric layer than anIDT electrode, in which the low velocity layer is positioned between thepiezoelectric layer and one of the high velocity layers. In certainapplications, other high impedance materials can be implemented in placeof the silicon layers 27 and/or 28 in the acoustic wave device 30, inwhich the other high impedance materials have a higher acousticimpedance than the acoustic impedance of a piezoelectric layer of thedevice. Example high impedance materials include silicon nitride,aluminum nitride, diamond such as synthetic diamond, quartz, spinel, andthe like. Similarly, the lithium tantalate layer 22 can be replaced byanother suitable piezoelectric layer, such as a lithium niobate layer,and such an acoustic wave device can function similarly to the acousticwave device 30 of FIG. 3A.

FIG. 3B illustrates a cross sectional view of an acoustic wave device 35according to an embodiment. The acoustic wave device 35 is like theacoustic wave device 20 of FIG. 2 except that the IDT electrode is analuminum IDT electrode 34 in the acoustic wave device 35. The aluminumIDT electrode 34 is on the opposite side of the lithium tantalate layer22 in the acoustic wave device 35 compared to the acoustic wave device30 of FIG. 3A.

FIG. 3C illustrates a graph comparing performance of the acoustic wavedevices 30 and 35 of FIGS. 3A and 3B, respectively. These simulationscorrespond to acoustic wave devices 30 and 35 having silicon highvelocity layers and a lithium tantalate piezoelectric layer. FIG. 3Cindicates that the acoustic wave device 35 has a betterelectromechanical coupling coefficient k² than the acoustic wave device30.

A variety of acoustic wave devices with high velocity layers and/or highimpedance layers on opposing sides of a piezoelectric layer can generatea boundary acoustic wave. Some examples acoustic wave devices arediscussed with reference to FIGS. 1 to 3B. Additional example acousticwave devices will be discussed with reference to FIGS. 4A to 4G. Anysuitable features of the acoustic wave devices disclosed herein can beimplemented together with each other.

FIG. 4A illustrates a cross sectional view of an acoustic wave device 40according to an embodiment. The acoustic wave device 40 is like theacoustic wave device 10 of FIG. 1 except that an additional low velocitylayer 41 is included between the second high velocity layer and thepiezoelectric layer 12. Although the acoustic wave device 40 isillustrated in a different orientation than the acoustic wave device 10,the way the devices are illustrated does not impact functionality of thedevices or imply an orientation of the physical device. The low velocitylayer 41 can alternatively be referred to as a low impedance layer. Thelow velocity layer 41 can be a silicon dioxide layer. In an embodimentof the acoustic wave device 40, the first high velocity layer 17 can bea silicon layer, the first low velocity layer 16 can be a silicondioxide layer, the second low velocity layer 41 can be a silicon dioxidelayer, and the second high velocity layer 18 can be a silicon layer.

FIG. 4B illustrates a cross sectional view of an acoustic wave device 42according to an embodiment. The acoustic wave device 42 is like theacoustic wave device 40 of FIG. 4A except that an adhesion layer 43 isincluded within the second low velocity layer 41 in the acoustic wavedevice 42. The adhesion layer 43 enhances adhesion strength betweenlayers of the acoustic wave device 42. The adhesion layer 43 can includea metal such as aluminum (Al), titanium (Ti), iron (Fe), or the like.When the adhesion layer 43 is metal, the adhesion layer 43 can improveinterlayer thermal conductivity and/or suppress self-heating of theacoustic wave device 42. In some instances, such an adhesion layer 43can enhance power durability of the acoustic wave device 42. Theadhesion layer 43 can be a dielectric material in some applications. Theadhesion layer 43 can be spaced from the piezoelectric layer 12 by asufficient distance such that the adhesion layer 43 does notsignificantly degrade transmission characteristics of the acoustic wavedevice 42. In the acoustic wave device 42, the second low velocity layer41 can be separated into a first portion and a second portion by theadhesion layer 43, in which the first portion is between thepiezoelectric layer 12 and the adhesion layer 43 and the second portionis between the adhesion layer 43 and the second high velocity layer 18.In an embodiment of the acoustic wave device 42, the first high velocitylayer 17 is a silicon layer, the first low velocity layer 16 is asilicon dioxide layer, the second low velocity layer 41 is a silicondioxide layer, and the second high velocity layer 18 is a silicon layer.

FIG. 4C illustrates a cross sectional view of an acoustic wave device 44according to an embodiment. The acoustic wave device 44 is like theacoustic wave device 40 of FIG. 4A except that an adhesion layer 45 isincluded within the first low velocity layer 16 in the acoustic wavedevice 44. The adhesion layer 45 enhances adhesion strength betweenlayers of the acoustic wave device 44. The adhesion layer 45 can includea metal such as aluminum, titanium, iron, or the like. When the adhesionlayer 45 is metal, the adhesion layer 45 can improve interlayer thermalconductivity and/or suppress self-heating of the acoustic wave device44. In some instances, such an adhesion layer 45 can enhance powerdurability of the acoustic wave device 44. The adhesion layer 45 can bea dielectric material in some applications. The adhesion layer 45 can bespaced from the piezoelectric layer 12 and the IDT electrode 14 by asufficient distance such that the adhesion layer 45 does notsignificantly degrade transmission characteristics of the acoustic wavedevice 44. In the acoustic wave device 44, the first low velocity layer16 can be separated into a first portion and a second portion by theadhesion layer 45, in which the first portion is between thepiezoelectric layer 12 and the adhesion layer 45 and the second portionis between the adhesion layer 45 and the first high velocity layer 17.In an embodiment of the acoustic wave device 44, the first high velocitylayer 17 is a silicon layer, the first low velocity layer 16 is asilicon dioxide layer, the second low velocity layer 41 is a silicondioxide layer, and the second high velocity layer 18 is a silicon layer.

FIG. 4D illustrates a cross sectional view of an acoustic wave device 46according to an embodiment. The acoustic wave device 46 is like theacoustic wave device 42 of FIG. 4B except that the acoustic wave device46 additionally includes the adhesion layer 45. Similarly, the acousticwave device 46 is like the acoustic wave device 44 of FIG. 4C exceptthat the acoustic wave device 46 additionally includes the adhesionlayer 43. Having adhesion layers 43 and 45 can improve adhesion oflayers of the acoustic wave device 46. Moreover, when the adhesionlayers 43 and 45 are metal, interlayer thermal conductivity can beimproved and/or self-heating can be suppressed. In an embodiment of theacoustic wave device 46, the first high velocity layer 17 is a siliconlayer, the first low velocity layer 16 is a silicon dioxide layer, thesecond low velocity layer 41 is a silicon dioxide layer, and the secondhigh velocity layer 18 is a silicon layer.

FIG. 4E illustrates a cross sectional view of an acoustic wave device 47according to an embodiment. As illustrated, the acoustic wave device 47includes a piezoelectric layer 12, an IDT electrode 14 on thepiezoelectric layer 12, a first high velocity layer 17 over the IDTelectrode 14 and the piezoelectric layer 12, a second high velocitylayer 18 on an opposite side of the piezoelectric layer 12 than the IDTelectrode 14, and a low velocity layer 41 positioned between thepiezoelectric layer 12 and the second high velocity layer 18. Anadhesion layer 43 is included within the low velocity layer 41. In anembodiment of the acoustic wave device 47, the first high velocity layer17 is a silicon layer, the first low velocity layer 16 is a silicondioxide layer, the second low velocity layer 41 is a silicon dioxidelayer, and the second high velocity layer 18 is a silicon layer. Anembodiment of the acoustic wave device 47 is similar to the acousticwave device 30 of FIG. 3A with the adhesive layer 43 added.

FIG. 4F illustrates a cross sectional view of an acoustic wave device 48according to an embodiment. The acoustic wave device 48 is like theacoustic wave device 10 of FIG. 1 except that the adhesive layer 45 isincluded within the low velocity layer 16 in the acoustic wave device48. In an embodiment of the acoustic wave device 48, the first highvelocity layer 17 is a silicon layer, the low velocity layer 16 is asilicon dioxide layer, and the second low velocity layer 18 is a siliconlayer. The adhesion layer 45 can improve adhesion between layers in theacoustic wave device 45. When the adhesion layer 45 is metal, interlayerthermal conductivity can be improved and/or self-heating can besuppressed.

FIG. 4G illustrates a cross sectional view of an acoustic wave device 49according to an embodiment. The acoustic wave device 49 is like theacoustic wave device 40 of FIG. 4A except that a second high velocitylayer 50 is shown as being a different material than the first highvelocity layer 17. As an example, the first high velocity layer 17 canbe a silicon layer and the second high velocity layer 50 can be a quartzlayer. Any other suitable combinations of high velocity layers can beimplemented. FIG. 4G is an illustrative example that an acoustic wavedevice in accordance with any suitable principles and advantagesdisclosed herein can include a first high velocity layer of a differentmaterial than a second high velocity layer. In an embodiment of theacoustic wave device 49, the first high velocity layer 17 is a siliconlayer, the first low velocity layer 16 is a silicon dioxide layer, thesecond low velocity layer 41 is a silicon dioxide layer, and the secondhigh velocity layer 50 is a quartz layer.

The high velocity layers, such as silicon layers, in embodimentsdiscussed herein can make acoustic waves impervious to externalinfluences. Accordingly, such acoustic wave devices can be stacked witheach other.

An acoustic wave device with a multi-layer piezoelectric substrate inaccordance with the principles and advantages discussed herein, forexample, with reference to FIGS. 1 to 3B and 4A to 4G, can beimplemented by a relatively thin structure. This can be advantageous forpackaging. For example, with relatively thin acoustic wave devices, twoor more die that include such acoustic wave devices can be stacked witheach other within a package. A radio frequency module that includes twostacked die with acoustic wave devices in accordance with the principlesand advantages disclosed herein can have a thickness of less than 300micrometers. In some instances, a radio frequency module that includesthree or more stacked die with acoustic wave devices in accordance withthe principles and advantages disclosed herein can have a thickness ofless than 300 micrometers. The stacked die can be over-molded withoutadditional protection in certain applications. Stacking can beimplemented at a device level, the die level, and/or at a module level.

FIG. 5 illustrates another cross sectional view of an acoustic wavedevice 55 according to an embodiment. The acoustic wave device 55 caninclude a multi-layer piezoelectric substrate in accordance with anysuitable principles and advantages discussed herein. The acoustic wavedevice 55 is thin. The acoustic wave device 55 is thinner than thecertain conventional SAW devices even if the thickness of the highacoustic velocity layers of the acoustic wave device 55 is sufficient toconfine the acoustic wave in the vicinity of the piezoelectric layer. Inan embodiment, the acoustic wave device 55 can include silicon highvelocity layers having thicknesses of around 5λ. Such an acoustic wavedevice 55 can have a thickness X₁ in a range from about 10 micrometers(um) to 100 um. As one example, the thickness X₁ can be about 40 um.Other acoustic wave devices disclosed above can also have a thickness ina range from 10 um to 100 um. In contrast, some present temperaturecompensated SAW (TCSAW) filters include an acoustic wave device with athickness of around 215 um. The higher end of the range for thethickness X₁ for the acoustic wave device 55 can be set by mechanicalruggedness considerations.

Relatively thin acoustic wave devices can be stacked in a filterassembly. This can reduce size of a packaged module that includesacoustic wave devices. With relatively thin acoustic wave devices, viascan be made through such devices. Stacked acoustic wave devices can beconnected to other components by electrical connections, such viasand/or wire bonds. Stacked acoustic wave devices can be included indifferent acoustic wave filters. Such acoustic wave filters can includeone or more ladder filters. The one or more ladder filters can includeseries and shunt one port acoustic wave resonators. FIGS. 6A to 6Eillustrate example stacked acoustic wave device assemblies. Any suitableprinciples and advantages of these examples can be implemented incombination with each other. Any of the acoustic wave devices discussedabove and/or any suitable combination of features of the acoustic wavedevices discussed above can be implemented in any of the example stackedacoustic wave device assemblies of FIGS. 6A to 6E.

FIG. 6A illustrates an acoustic wave device assembly 60 of stackedacoustic wave devices according to an embodiment. The acoustic wavedevice assembly 60 is compact and has a relatively small size. Asillustrated, the acoustic wave device assembly 60 includes die 61, 62,and 63, vias 64, 65, and 66, contacts 67, and a packaging substrate 68.The die 61, 62, and 63 are stacked with each other. Each of these diecan include one or more acoustic wave devices in accordance with anysuitable principles and advantages discussed herein. Vias 64, 65, and 66can provide electrical connections between die 61, 62, and 63,respectively, and contacts 67 on the packaging substrate 68. Via holesthrough relatively thin piezoelectric layers and acoustic wave devicescan be implemented more easily than though thicker layers and devices.The packaging substrate 68 can be a laminate substrate that includesmetal routing.

FIG. 6B illustrates an acoustic wave device assembly 70 of stackedacoustic wave devices according to an embodiment. The acoustic wavedevice assembly 70 includes die 61, 62, and 63, vias 64, 65, and 66,contacts 67, a packaging substrate 68, and air gaps 71 and 72 betweendie. The acoustic wave device assembly 70 includes stacked die with avia though at least one of the die. As illustrated, the via 64 extendsthough die 62 and 63 and the via 65 extends through die 63. The die 61and 62 are suspended over air gaps 71 and 72, respectively. The air gaps71 and 72 can improve electrical isolation of each die relative to theacoustic wave device assembly 60 of FIG. 6A.

FIG. 6C illustrates an acoustic wave device assembly 75 of stackedacoustic wave devices according to an embodiment. The acoustic wavedevice assembly 75 includes die 61, 62, and 63, vias 64, 65, and 66,contacts 67, a packaging substrate 68, and dielectric layers 76 and 77.The acoustic wave device assembly 75 includes stacked die with a viathough at least one of the die. The dielectric layers 76 and 77 canelectrically isolate the die from each other. For example, thedielectric layer 76 provides electrical isolation between the die 61 andthe die 62. As another example, the dielectric layer 77 provideselectrical isolation between the die 62 and the die 63. The dielectriclayers 76 and 77 can maintain mold strength of a packaged device.

FIG. 6D illustrates an acoustic wave device assembly of stacked acousticwave devices 80 according to an embodiment. The acoustic wave deviceassembly 80 includes die 61, 62, and 63, vias 64, 65, and 66, contacts67, a packaging substrate 68, dielectric layers 81 and 83, and shieldinglayers 82 and 84. The acoustic wave device assembly 80 includes stackeddie with a via though at least one of the die. A dielectric layer andshielding layer between the dies can electrically isolate and shield thedies from each other. For example, the dielectric layer 81 and theshielding layer 82 can provide electrical isolation and shieldingbetween the die 61 and the die 62. As another example, the dielectriclayer 83 and the shielding layer 84 can provide electrical isolation andshielding between the die 62 and the die 63. The shielding layers 82 and84 can be implemented by any suitable shielding metal layers.

FIG. 6E illustrates an acoustic wave device assembly 85 of stackedacoustic wave devices according to an embodiment. The acoustic wavedevice assembly 85 includes die 61, 62, and 63, wire bonds 86, 87, and88, and a packaging substrate 68. The wire bonds 86, 87, and 88 canprovide electrical connections between die 61, 62, and 63, respectively,and the packaging substrate 68. A wire bonds 86, 87, and 88 can eachextend from a respective wire bond pad on die 61, 62, and 63 to arespective pad on the packaging substrate 68. Wire bonds and viasextending through a die can be implemented with each other in some otherembodiments to provide electrical connections between one or more dieand metal routing of a packaging substrate. An air gap and/or adielectric layer and/or a shielding layer can be implemented between dieof a stacked acoustic wave assembly, in which one or more of the die hasa wire bond extending therefrom.

The acoustic wave devices and/or acoustic wave device assembliesdiscussed herein can be implemented in a variety of packaged modules.Some example packaged modules will now be discussed in which anysuitable principles and advantages of the acoustic wave devicesdiscussed herein can be implemented. The example packaged modules caninclude a package that encloses the illustrated circuit elements. Theillustrated circuit elements can be disposed on a common packagingsubstrate. The packaging substrate can be a laminate substrate, forexample. FIGS. 7A, 7B, and 7C are schematic block diagrams ofillustrative packaged modules according to certain embodiments. Anysuitable combination of features of these packaged modules can beimplemented together with each other.

FIG. 7A is a schematic block diagram of a module 90 that includesfilters 91 and an antenna switch 92. The module 90 can include a packagethat encloses the illustrated elements. The filters 91 and the antennaswitch 92 can be disposed on a common packaging substrate. The packagingsubstrate can be a laminate substrate, for example. The filters 91 caninclude one or more suitable acoustic wave devices disclosed herein. Thefilters 91 can include die stacked with each other, in which the dieinclude one or more acoustic wave devices disclosed herein. The antennaswitch 92 can be a multi-throw radio frequency switch. The antennaswitch 92 can electrically couple a selected filter of the filter 91 toan antenna port of the module 90. The filters 91 can include two or moreacoustic wave filters coupled together at a common node and arranged asa multiplexer. Such a multiplexer can be a duplexer, a quadplexer, ahexaplexer, an octoplexer, or the like.

FIG. 7B is a schematic block diagram of a module 94 that includesfilters 91, a radio frequency switch 96, and a power amplifier 97. Thepower amplifier 97 can amplify a radio frequency signal. The radiofrequency switch 96 can electrically couple an output of the poweramplifier 97 to a selected filter of the filters 91. The filters 91 caninclude one or more acoustic wave devices disclosed herein. The filters91 can include die stacked with each other, in which the die include oneor more acoustic wave devices disclosed herein. The filters 91 caninclude two or more acoustic wave filters coupled together at a commonnode and arranged as a multiplexer. Such a multiplexer can be aduplexer, a quadplexer, a hexaplexer, an octoplexer, or the like.

FIG. 7C is a schematic block diagram of a module 98 that includes apower amplifier 97, a radio frequency switch 96, filters 91, and anantenna switch 92. The module 98 is similar to the module 94 of FIG. 7B,except the module 98 additionally includes the antenna switch 92.

Any of the acoustic wave devices, acoustic wave device assemblies,and/or packaged modules can be implemented in a wireless communicationdevice. FIG. 8 is a schematic block diagram of a wireless communicationdevice 100 that includes filters 103 in accordance with one or moreembodiments. The wireless communication device 100 can be any suitablewireless communication device. For instance, a wireless communicationdevice 100 can be a mobile phone, such as a smart phone. As illustrated,the wireless communication device 100 includes an antenna 101, an RFfront end 102, an RF transceiver 104, a processor 105, a memory 106, anda user interface 108. The antenna 101 can transmit RF signals providedby the RF front end 102. Such RF signals can include carrier aggregationsignals. The antenna 101 can provide received RF signals to the RF frontend 102 for processing. The wireless communication device 100 caninclude two or more antennas in certain instances.

The RF front end 102 can include one or more power amplifiers, one ormore low noise amplifiers, RF switches, receive filters, transmitfilters, duplex filters, filters of a multiplexer, filters of adiplexers or other frequency multiplexing circuit, or any suitablecombination thereof. The RF front end 102 can transmit and receive RFsignals associated with any suitable communication standards. Any of theacoustic wave devices disclosed herein can be implemented in the filters103 of the RF front end 102. Any of the acoustic wave device assembliesdisclosed herein can implement one or more of the filters 103.Accordingly, the filters 103 can include a relatively thin acoustic wavedevice arranged to generate a boundary acoustic wave.

The RF transceiver 104 can provide RF signals to the RF front end 102for amplification and/or other processing. The RF transceiver 104 canalso process an RF signal provided by a low noise amplifier of the RFfront end 102. The RF transceiver 104 is in communication with theprocessor 105. The processor 105 can be a baseband processor. Theprocessor 105 can provide any suitable base band processing functionsfor the wireless communication device 100. The memory 106 can beaccessed by the processor 105. The memory 106 can store any suitabledata for the wireless communication device 100. The user interface 108can be any suitable user interface, such as a display with touch screencapabilities.

Any of the embodiments described above can be implemented in associationwith mobile devices such as cellular handsets. The principles andadvantages of the embodiments can be used for any systems or apparatus,such as any uplink cellular device, that could benefit from any of theembodiments described herein. The teachings herein are applicable to avariety of systems. Although this disclosure includes some exampleembodiments, the teachings described herein can be applied to a varietyof structures. Any of the principles and advantages discussed herein canbe implemented in association with RF circuits configured to processsignals having a frequency in a range from about 30 kHz to 300 GHz, suchas in a range from about 450 MHz to 6 GHz. Acoustic wave filtersdisclosed herein can be band pass filters having a passband that iswithin a frequency range from about 450 MHz to 6 GHz. Acoustic wavefilters disclosed herein can filter RF signals at frequencies up to andincluding millimeter wave frequencies.

Aspects of this disclosure can be implemented in various electronicdevices. Examples of the electronic devices can include, but are notlimited to, consumer electronic products, parts of the consumerelectronic products such as die and/or acoustic wave filter assembliesand/or packaged radio frequency modules, uplink wireless communicationdevices, wireless communication infrastructure, electronic testequipment, etc. Examples of the electronic devices can include, but arenot limited to, a mobile phone such as a smart phone, a wearablecomputing device such as a smart watch or an ear piece, a telephone, atelevision, a computer monitor, a computer, a modem, a hand-heldcomputer, a laptop computer, a tablet computer, a personal digitalassistant (PDA), a microwave, a refrigerator, an automobile, a stereosystem, a DVD player, a CD player, a digital music player such as an MP3player, a radio, a camcorder, a camera, a digital camera, a portablememory chip, a washer, a dryer, a washer/dryer, a copier, a facsimilemachine, a scanner, a multi-functional peripheral device, a wrist watch,a clock, etc. Further, the electronic devices can include unfinishedproducts.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,”“include,” “including” and the like are to be construed in an inclusivesense, as opposed to an exclusive or exhaustive sense; that is to say,in the sense of “including, but not limited to.” The word “coupled”, asgenerally used herein, refers to two or more elements that may be eitherdirectly connected, or connected by way of one or more intermediateelements Likewise, the word “connected”, as generally used herein,refers to two or more elements that may be either directly connected, orconnected by way of one or more intermediate elements. Additionally, thewords “herein,” “above,” “below,” and words of similar import, when usedin this application, shall refer to this application as a whole and notto any particular portions of this application. Where the contextpermits, words in the above Detailed Description using the singular orplural number may also include the plural or singular numberrespectively. The word “or” in reference to a list of two or more items,that word covers all of the following interpretations of the word: anyof the items in the list, all of the items in the list, and anycombination of the items in the list.

Moreover, conditional language used herein, such as, among others,“can,” “could,” “might,” “may,” “e.g.,” “for example,” “such as” and thelike, unless specifically stated otherwise, or otherwise understoodwithin the context as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements and/or states. Thus, such conditional language is notgenerally intended to imply that features, elements and/or states are inany way required for one or more embodiments.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the disclosure. Indeed, the novel apparatus, methods, andsystems described herein may be embodied in a variety of other forms;furthermore, various omissions, substitutions and changes in the form ofthe methods and systems described herein may be made without departingfrom the spirit of the disclosure. For example, while blocks arepresented in a given arrangement, alternative embodiments may performsimilar functionalities with different components and/or circuittopologies, and some blocks may be deleted, moved, added, subdivided,combined, and/or modified. Each of these blocks may be implemented in avariety of different ways. Any suitable combination of the elements andacts of the various embodiments described above can be combined toprovide further embodiments. The accompanying claims and theirequivalents are intended to cover such forms or modifications as wouldfall within the scope and spirit of the disclosure.

What is claimed is:
 1. An acoustic wave device comprising: apiezoelectric layer; an interdigital transducer electrode on thepiezoelectric layer; high velocity layers on opposing side of thepiezoelectric layer, the high velocity layers including a first highvelocity layer having a first acoustic velocity and a second highvelocity layer having a second acoustic velocity; and a temperaturecompensation layer positioned between the first high velocity layer andthe piezoelectric layer, the acoustic wave device being configured togenerate a boundary acoustic wave having a velocity that is less thanboth the first acoustic velocity and the second acoustic velocity. 2.The acoustic wave device of claim 1 wherein the first acoustic velocityis substantially the same as the second acoustic velocity.
 3. Theacoustic wave device of claim 1 wherein the first acoustic velocity isdifferent than the second acoustic velocity.
 4. The acoustic wave deviceof claim 1 wherein the first high velocity layer is a silicon layer. 5.The acoustic wave device of claim 4 wherein the second high velocitylayer is a second silicon layer.
 6. The acoustic wave device of claim 1wherein the first high velocity layer includes at least one of siliconnitride, aluminum nitride, diamond, quartz, or spinel.
 7. The acousticwave device of claim 1 wherein the piezoelectric layer is either alithium tantalate layer or a lithium niobate layer.
 8. The acoustic wavedevice of claim 1 wherein the temperature compensation layer includessilicon dioxide.
 9. The acoustic wave device of claim 1 wherein theboundary acoustic wave has a wavelength of λ and the first high velocitylayer has a thickness in a range from 1λ to 10λ.
 10. The acoustic wavedevice of claim 1 wherein the interdigital transducer electrode is incontact with the piezoelectric layer on a side of the piezoelectriclayer facing the temperature compensation layer.
 11. The acoustic wavedevice of claim 1 wherein the interdigital transducer electrode is incontact with the piezoelectric layer on a side of the piezoelectriclayer that is opposite to the temperature compensation layer.
 12. Theacoustic wave device of claim 1 wherein the boundary acoustic wave has awavelength of λ and the piezoelectric layer has a thickness of less than2λ.
 13. An acoustic wave device comprising: a piezoelectric layer; aninterdigital transducer electrode on the piezoelectric layer; siliconlayers on opposing sides of the piezoelectric layer; and a silicondioxide layer disposed between one of the silicon layers and thepiezoelectric layer, the acoustic wave device being configured togenerate a boundary acoustic wave at an interface of the piezoelectriclayer and the interdigital transducer electrode.
 14. The acoustic wavedevice of claim 13 wherein the boundary acoustic wave has a wavelengthof λ and the silicon layers each have a thickness in a range from λ to10λ.
 15. The acoustic wave device of claim 14 wherein the boundaryacoustic wave has a wavelength of λ and the piezoelectric layer has athickness of no greater than 2λ.
 16. The acoustic wave device of claim13 wherein the piezoelectric layer is a lithium tantalate layer.
 17. Theacoustic wave device of claim 13 wherein the piezoelectric layer is alithium niobate layer.
 18. The acoustic wave device of claim 13 whereinthe interdigital transducer electrode is on a side of the piezoelectriclayer facing the silicon dioxide layer.
 19. The acoustic wave device ofclaim 13 wherein the interdigital transducer electrode is on a side ofthe piezoelectric layer opposite to the silicon dioxide layer.
 20. Anacoustic wave filter comprising an acoustic wave device that includes apiezoelectric layer, an interdigital transducer electrode on thepiezoelectric layer, silicon layers on opposing sides of thepiezoelectric layer, and a silicon dioxide layer disposed between one ofthe silicon layers and the piezoelectric layer, the acoustic wave devicebeing configured to generate a boundary acoustic wave, and the acousticwave filter configured to filter a radio frequency signal.